Cook the sliced sausages in the oil until brown. Add onions, and allow to caramelize until golden brown. Add cabbage, stir to combine. Add garlic, stir to combine. Add salt and pepper to taste. Allow to cook for a few minutes, then add the Oktoberfest beer. Allow lager to reduce for about 3 minutes. Add potatoes and hot vegetable stock. Cover and let simmer for 30-40 minutes. Add in the vinegar just before serving, stir well and enjoy!